Energy Factor (EF) is a rating that measures how efficiently a water heater converts energy into hot water over a typical day, accounting for heating efficiency and standby losses. It is a legacy metric now largely replaced by Uniform Energy Factor (UEF). For HVAC systems, efficiency is measured with ratings like SEER/EER for cooling and AFUE or HSPF for heating. Understanding these ratings helps compare equipment energy use and long-term operating costs.
/ˈɛnərdʒi ˈfæktər (EF)/
Energy Factor (EF) is a rating that measures how efficiently a water heater converts energy into hot water over a typical day, accounting for heating efficiency and standby losses. It is a legacy metric now largely replaced by Uniform Energy Factor (UEF). For HVAC systems, efficiency is measured with ratings like SEER/EER for cooling and AFUE or HSPF for heating. Understanding these ratings helps compare equipment energy use and long-term operating costs.
What does EF mean and how is it different from HVAC ratings?
EF measures water heater efficiency, while HVAC uses SEER/EER for cooling and AFUE/HSPF for heating efficiency.
Source: The Cooling Company
Efficiency ratings compare energy use across systems.
A homeowner compares a high-UEF water heater and a higher-SEER HVAC system, choosing models that cut utility bills without sacrificing comfort.
Use EF/UEF for water heaters and SEER/EER/HSPF/AFUE for HVAC, and match equipment to proper sizing and installation for real savings.
“Use EF/UEF for water heaters and SEER/EER/HSPF/AFUE for HVAC, and match equipment to proper sizing and installation for real savings.”
DOE shifted from EF to UEF to better reflect real-world water heater usage patterns.
Is EF still used for new water heaters?
Most new models use UEF, but EF still appears in older listings.
What efficiency rating should I use for HVAC?
Use SEER/EER for cooling and AFUE or HSPF for heating.
Do higher ratings always save money?
Usually, but only when equipment is properly sized and installed.
Need help with energy factor (ef)? Our licensed technicians in Las Vegas are ready to assist.
Fill out the form below. We typically respond within minutes.
